Rapid cabin heating of a motor vehicle is desired, particularly during cold ambient conditions, to provide passenger comfort. Classically, cabin heat comes from the engine coolant, which may be heated indirectly via a massive increase in exhaust heat. However, such a method is energy inefficient and wastes fuel, as only a small fraction of the exhaust heat appears in the engine coolant.
The inventors have recognized that exhaust heat whose route is altered by throttling the exhaust may be recovered and directly routed to the cabin heating system rather than indirectly routed to the cabin heating system via the engine coolant system. Accordingly, a method for heating a vehicle cabin is provided, comprising closing an exhaust throttle while diverting at least a portion of throttled exhaust gas through an exhaust gas recirculation (EGR) cooler coupled upstream of the throttle, and transferring heat from the EGR cooler to a heater core configured to provide heat to the vehicle cabin.
In this way, the exhaust may be throttled to route the exhaust flow through an EGR cooler, and the exhaust heat may be transferred to the cabin heating system coolant via the EGR cooler. By doing so, the cabin heating system heater core may be provided with early exhaust heat directly, rather than the early exhaust heat being dissipated via the engine and contacting surfaces. As such, energy used to heat the vehicle cabin may be reduced, increasing fuel economy.
Thus, in the above-described method, exhaust heat may be prioritized for cabin heating over engine heating. In fact, the engine coolant could be ice cold and this system would still provide cabin heat extracted from engine exhaust. This may have multiple advantages. First, it provides rapid cabin heating at start. Second, it provides an effective method of getting the exhaust heat to the cabin heater core, which is crucial for idling conditions in cold ambient temperatures. Further, when enough coolant heat is available for cabin heating, the system works conventionally. In this conventional case, one would cease to throttle the exhaust to route it through the EGR cooler. Should EGR cooling be called for, the cabin has first priority use of this extracted heat. If cabin heat is not called for, the heat is added to the coolant system.
Further, in some examples, exhaust condensation in the exhaust to a water heat exchanger may be intentional. This gives improved heat transfer from the exhaust to heat exchanger due to the heat of vaporization. In some examples, the controller may adjust operation so the exhaust flow is not allowed to flow into the engine intake system (EGR) until the heat exchanger's (EGR cooler) temperature is high enough to avoid condensation. But exhaust condensation in the exhaust path is an occurrence on most, if not all, engine starts.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.